This invention relates in general to guidewires, and in particular to a small diameter steerable guidewire for use in procedures in narrow vascular lumens, such as percutaneous transluminal coronary angioplasty (PTCA).
The use of small dimension guidewires in cardiovascular systems has become an absolute necessity. It is difficult to penetrate the stenotic areas within regions of narrow lumens by the use of conventional guidewires, therefore, the traumatic risk to the patient increases with the decrease of available lumen area. Narrower guidewires lessen this risk. Additionally, a very low thrombogenicity, traumatic sensitive torque control, equal unidirectional flexibility, radiopacity, low friction, constant diameter, smooth transition among its segmented parts, being shapeable to a desired configuration and having an equal bending sensitivity in all directions along the length of its distal end are highly desirable features in a small diameter guidewire.
Small diameter guidewires having diameters less than 0.02 inch are known in the art as disclosed in U.S. Pat. No. 4,545,390. In the steerable guidewire disclosed in this patent, the main wire has a Teflon coated core wire, formed with a tapered region at its distal region. A helically wound spring is attached to the tapered region and is shown extending beyond the tapered distal region to a rounded tip. The diameter of the core wire and helically wound spring at its distal region does not exceed 0.02 inch.
A similar guidewire is shown in U.S. Pat. No. 4,538,622. This guidewire is again formed with a main core wire having a tapered distal region. The main wire is wrapped at its tapered distal end by two coils, at least one coil being of a radio opaque material. The coils extend beyond the distal end of the tapered wire, and the diameter of the distal end wire with coils is less than 0.02 inch. In U.S. Pat. No. 4,554,929 a similar Teflon coated core wire having a tapered distal region includes a spring on the tapered region which extends beyond the distal end thereof. A rounded tip 21 is secured to the distal end of the spring and is coupled to the tapered region by a safety wire.
These prior art guidewires have been satisfactory; however, they suffer from the disadvantage that they have limited flexibility in regions of the distal end and do not have uniform directional flexibility along the length of the spring coil.
Accordingly, it is desirable to provide a small diameter guidewire for use in cardiovascular vessels having improved flexibility and increased uniform directional bendability along the length of the coil spring region of increased flexibility.